Magnetic hard disk drives typically include one or more rotating magnetic data storage disks defining a multiplicity of concentric data tracks. Magnetic disk drives having high track and bit densities most frequently rely upon voice coil actuators for moving a selected data transducer (head) from a departure track to a destination track location during track seeking operations, for settling the head at the vicinity of the destination track during track settling operations, and for following the centerline of the destination track during track following operations when user data may be written or read from the disk.
Voice coil actuators are typically part of a head position servo loop. In one approach pertinent to the present invention, actual head position information is sampled by the head from the user data storage surface of the disk as the head passes over each one of a series of embedded servo sectors. A servo data detector circuit detects coarse head position information, digitally quantizes fine head position information, and sends the coarse and fine information to a servo controller, which may include a programmed disk drive microcontroller. A state model of the head positioner is developed in firmware, based upon the coarse and fine positional samples and commanded head position; and, driving currents are generated and applied to the voice coil to move the head in a highly controlled fashion.
It is known to arrange the concentric data tracks of a hard disk drive into contiguous data zones, wherein each zone is given a data transfer rate adapted to the innermost data track radius of the zone (the innermost track having the highest bit density at a constant data transfer rate throughout the zone). At the expense of circuit complexity of the read channel necessitated by changing clocking rates and read channel equalization with changes in zones, this approach significantly increases the data storage capacity, by recognizing that more storage space, and more data, is available in radially outer zones, than is available within inner zones. A track of an outer zone may typically include twice as much data as a track of an inner zone. Accordingly, the outermost zone may have a data transfer rate two times the data transfer rate of the innermost zone.
One presently preferred example of a hard disk drive architecture employing embedded head position servo and zone data recording techniques with constant frequency embedded servo sectors and split data fields is provided by commonly assigned U.S. Pat. No. 5,255,136, the disclosure thereof being incorporated herein by reference.
Advantages of using a PRML sampled data channel are known in connection with magnetic hard disk drives. One example of a disk drive architecture employing a PRML Class IV sampled data channel is described in commonly assigned, copending U.S. patent application Ser. No. 07/937,064 filed on Aug. 27, 1992, entitled: "Disk Drive Using PRML Class IV Sampling Data Detection with Digital Adaptive Equalization", the disclosure thereof being incorporated herein by reference. While the approach followed in this prior patent works satisfactorily, one drawback attending the described approach relates to the asynchronous, constant frequency embedded servo sectors.
In this prior patent, the servo information was recorded at a constant frequency across the radial extent of the drive, and was asynchronous with respect to the data fields which were coded to match a PR Class IV (1-D.sup.2) spectrum. Because the servo sectors were asynchronous with respect to user data, special digital peak detection circuitry was provided to detect and decode the servo information. Also, the analog filter equalizer, and the digital finite impulse response filter had to be retuned in real time at the arrival of each embedded servo sector, adding to the complexity of the design and control of the drive. Since the servo sectors were recorded at a constant frequency in accordance with the teachings of commonly asssigned U.S. Pat. No. 5,170,299, the disclosure thereof being incorporated herein by reference, considerable data storage space was lost, considering that the data tracks are arranged into concentric zones on the disk surface.
These drawbacks have resulted in a hitherto unsolved need for a synchronous sampled data channel servo data detection method and apparatus which is more compatible with the synchronous read channel architecture.